Thermoplastic vulcanizates (“TPVs”) are vulcanized compositions that include finely dispersed crosslinked elastomeric particles in a continuous thermoplastic phase. TPVs are produced by a process called dynamic vulcanization where the elastomeric component is selectively crosslinked during melt mixing under conditions of shear and temperature with the thermoplastic resins. TPVs have the benefits of the elastomeric properties provided by the elastomer phase and the processability provided by the thermoplastic phase.
Conventional TPVs are made using polypropylene as a thermoplastic component. The polypropylene typically has a fractional melt flow rate, such as a melt flow rate of less than 1 g/10 min, and a narrow molecular weight distribution, such as from about 2 to 4. However, TPVs containing such fractional polypropylenes can be difficult to process. That is, when producing either the TPV or a final end-use article comprising the TPV, the production equipment can be rate limited by the high viscosity of the polypropylene phase due to (i) the increased gear box torque and/or pressures that result from extruding the high viscosity polypropylene, and/or (ii) the increased melt temperatures needed to process the high viscosity polypropylene.
As described in PCT Publication No. WO 99/64510, attempts have been made to produce TPVs with improved processability using a mixture of olefinic rubber and a polypropylene blend composition having a melt flow rate of 0.5 to 5 g/10 min and a Mw/Mn of 5.5 to 20. However, the need to prepare a mixture of polypropylenes complicates the manufacturing process. PCT Publication No. WO 99/64510 also describes the use of reactor blended polypropylenes. However, the reactor blended polypropylenes in PCT Publication No. WO 99/64510 have a low molecular weight which can negatively impact physical properties of the TPV, such as tensile properties and melt strength.
Additional background references include PCT Publication Nos. WO 2014/070384; WO 2014/070385; and WO 2014/070386.
Therefore, there is still a need for TPVs that have improved extruder processability for the consumer as well as ease of manufacture without sacrificing the mechanical properties of the TPV.